Method of manufacturing semiconductor wafer, semiconductor wafer manufactured by the same, semiconductor epitaxial wafer, and method of manufacturing the semiconductor epitaxial wafer

ABSTRACT

There is disclosed a method of manufacturing a semiconductor wafer which has a dopant evaporation preventive film formed on one of main surfaces thereof, wherein a film serving as the dopant evaporation preventive film is formed on the one of the main surface by a plasma CVD method. There is also disclosed a method of manufacturing a semiconductor wafer having a plasma CVD film on one of main surfaces, wherein the plasma CVD film is formed on the one of the main surfaces of the semiconductor wafer so that a stress between the plasma CVD film and the semiconductor wafer falls in a range of 1×10 8  -1×10 9  dyne/cm 2 . Finally, a semiconductor wafer is disclosed having a plasma CVD film formed on only one face that serves as a barrier to autodoping during processing and which may function to create within the semiconductor wafer a strained layer that can getter impurities.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of manufacturing a semiconductorwafer and a semiconductor wafer manufactured by the method, andparticularly to a method of manufacturing a semiconductor wafer having afilm formed through plasma chemical vapor deposition (hereinafterreferred to as plasma CVD) and a semiconductor wafer manufactured by themethod. Further, the present invention relates to a semiconductorepitaxial wafer, or a semiconductor wafer on which an epitaxial layer isgrown, and a method of manufacturing the same.

2. Description of the Related Art

In an epitaxial growth process wherein a thin monocrystalline siliconfilm is grown on a silicon wafer in gas phase, the silicon wafer isusually exposed to a high temperature of not less than 1000° C. Duringthis process, a dopant evaporated from the silicon wafer is incorporatedinto a growing epitaxial layer through a gas phase. This phenomenon istypically termed autodoping. When autodoping is prominent, an epitaxiallayer having a desired resistivity cannot be obtained. Consequently, asemiconductor element having this epitaxial layer becomes defective dueto a failure to exhibit designed characteristics.

Autodoping becomes prominent when the resistivity of a silicon wafer isrelatively low. Therefore, according to a generally employed method,when an epitaxial layer is formed on a wafer having a relatively lowresistivity, a silicon oxide film (hereinafter abbreviated to an "oxidefilm"), serving as a film that prevents autodoping (a dopant evaporationpreventive film), is formed on one of the main surfaces of a siliconwafer (hereinafter referred to as a "back surface") on which noepitaxial layer is grown.

A conventionally used oxide film to be formed on the back surface is:

1) an atmospheric pressure chemical vapor deposition (atmosphericpressure CVD) oxide film grown in an atmospheric pressure CVD system, or

2) a thermal oxide film grown through oxidation within a heat treatmentfurnace.

However, either of the oxide films causes a relatively large stress to asilicon wafer, resulting in a potential warpage of the silicon wafer orcrystal defects in the silicon wafer. Furthermore, in the case of athermal oxide film, since a dopant doped in a silicon wafer isincorporated into the thermal oxide film during the formation of thethermal oxide film, autodoping occurs due to dopant being released fromthe thermal oxide film during a subsequent epitaxial growth process.Therefore, the thermal oxide film fails to properly function as a filmthat prevents autodoping.

In addition, when either of the oxide films is formed, the oxide film isformed not only on the back surface of a silicon wafer but also on theother main surface (hereinafter referred to as a "front surface") onwhich an epitaxial layer is grown. Accordingly, after completion of aprocess of forming the oxide film, the oxide film formed on the frontsurface must be removed.

An oxide film formed on the front surface is generally removed bypolishing. However, since the polishing speed of an oxide film is muchslower than the polishing speed of a silicon, it takes a very long timeto polish off a thermal oxide film which covers the entire front surfaceof a silicon wafer. Furthermore, uneven polishing is very likely tooccur, resulting in a decreased degree of flatness of the silicon wafer.In the case of an atmospheric pressure CVD oxide film, which is formedpartially extending onto the front surface, polishing off such an excessportion of the oxide film also causes the degree of the flatness of asilicon wafer to decrease.

In order to avoid these problems, etching off an oxide film only fromthe front surface while protecting an oxide film on the back surface maybe performed. Alternatively, an oxide film may be removed from the frontsurface by surface grinding, and then the front surface may be polished.However, these methods require an additional process, resulting in anincreased cost of manufacture.

Along with a recent tendency to increase the degree of integration andprecision of semiconductor devices, there has been an increasing demandfor silicon wafers having a diameter of not less than 200 mm. When anepitaxial layer is to be grown on a silicon wafer having a largediameter of not less than 200 mm, a low temperature epitaxial growthprocess is applied in order to obtain a uniform thickness and a uniformresistivity distribution in an epitaxial layer, to reduce a transitionwidth (the width of a region which is located in the vicinity of theboundary between an epitaxial layer and a silicon wafer, each having adifferent dopant concentration, and in which a dopant concentrationtransits), to reduce contamination with metal atoms, etc. In order toobtain such a quality, a wafer subjected to a low temperature epitaxialgrowth process is required to further improve its degree of flatness andreduce its warpage as compared with a wafer to be subjected to aconventional high temperature epitaxial growth process.

However, as mentioned previously, when an atmospheric pressure CVD oxidefilm or a thermal oxide film is used as a protective film formed on theback surface of a silicon wafer, the degree of flatness of a frontsurface deteriorates, and a relatively large stress acts on the siliconwafer, resulting in an increased warpage of the silicon wafer. Thiseffect is particularly noticeable with a silicon wafer having a largediameter. Therefore, there arises a problem when such a wafer issubjected to a photolithographic process, which strictly requires a highdegree of flatness. Further, too large a stress causes crystal defectsin a wafer.

A layer formed on the back surface of a silicon wafer is also utilizedas a gettering layer for gettering heavy metals and the like.

Gettering is a technique for collecting impurities, such as heavy metal,which are generated in the course of manufacturing semiconductor devicesfrom a silicon wafer, to outside of a device region on the front surfaceof a silicon wafer, thereby preventing device characteristics fromdegradation.

According to a typical gettering method, polycrystalline silicon isdeposited on the back surface of a silicon wafer to form a getteringlayer. In order to deposit polycrystalline silicon so as to form agettering layer, a low pressure CVD method is usually carried out.However, the growth of polycrystalline silicon causes stress to act on awafer, resulting in a larger warpage of the wafer as compared with awafer having no polycrystalline silicon layer. Also, the warpage of awafer increases when the diameter of the wafer increases if apolycrystalline silicon layer is grown in a same condition.

Also, as a wafer having a polycrystalline silicon layer is subjected toheat treatment in the course of the fabrication of devices, thepolycrystalline silicon is gradually crystallized into monocrystal,resulting in a less gettering capability.

A silicon wafer utilized from manufacturing semiconductor devices isrequired to have and maintain a gettering capability during themanufacture of semiconductor devices. In this connection, there is aproblem that the warpage of a wafer increases with the diameter of thewafer.

In order to improve a gettering capability, in a silicon wafer having apolycrystalline silicon layer as a gettering layer on the back surfacethereof, a stress acting on the wafer must be increased. Therefore, animprovement in the gettering capability and a reduction in stress, i.e.a reduction in warpage, cannot be achieved simultaneously. Furthermore,as heat treatment progresses during the manufacture of semiconductordevices, a polycrystalline silicon layer is gradually crystallized intomonocrystal, resulting in difficulty in maintaining the getteringcapability.

When an epitaxial layer is to be formed on a silicon wafer having a lowdopant concentration, formation of a gettering layer on the back surfaceof the wafer is sufficient because there is no problem of autodoping.However, when a silicon wafer having a high dopant concentration isused, a protective film which has both a gettering capability and anautodoping preventive capability must be formed on the back surface ofthe wafer.

However, when a polycrystalline silicon layer is formed on a backsurface of a silicon wafer having a high dopant concentration, agettering effect is obtained, but an autodoping preventive capability isnot obtained, since a dopant released from the silicon wafer readilydiffuses through the polycrystalline silicon layer.

When an atmospheric pressure CVD oxide film is formed on a siliconwafer, an effect that prevents autodoping is obtained, and a getteringeffect is also obtained since a stress acts between the silicon waferand the oxide film. However, due to difficulty in controlling thestress, the warpage of the silicon wafer tends to be increased.

SUMMARY OF THE INVENTION

This invention has been accomplished in view of the above-mentionedproblems, and it is an object of the present invention to provide animproved semiconductor wafer having an autodoping preventive film, inwhich even when the semiconductor wafer has a large diameter of not lessthan 200 mm, the stress acting to the wafer and resultant warpage of thewafer can be decreased while maintaining a uniform thicknessdistribution, a uniform resistivity distribution and a narrow transitionwidth of an epitaxial layer grown on the semiconductor wafer, and inwhich the front surface of the semiconductor wafer can have an excellentdegree of flatness without requiring an extra process such as a processof etching off an oxide film from the front surface.

Another object of the present invention is to provide a semiconductorwafer which has an excellently persistent gettering capability, anautodoping preventive capability and a small stress acting thereon witha resultant small warpage thereof.

A further object of the present invention is to provide a semiconductorepitaxial wafer comprising the above-described semiconductor wafer andan epitaxial layer grown thereon, and a method of manufacturing thesame.

According to an aspect of the present invention, there are provided:

1) a method of manufacturing a semiconductor wafer which has a dopantevaporation preventive film formed on one of main surfaces thereof,wherein a film serving as the dopant evaporation preventive film isformed on the one of the main surfaces by a plasma CVD method;

2) a method of manufacturing a semiconductor wafer in which a dopantevaporation preventive film is formed on one of main surfaces and asemiconductor thin film is formed on the other main surface by epitaxialgrowth, wherein a film serving as the dopant evaporation preventive filmis formed on the one of the main surfaces by a plasma CVD method, andthe semiconductor wafer is subject to heat treatment at a temperaturelower than a temperature at which the epitaxial growth of thesemiconductor thin film is carried out;

3) a method of manufacturing a semiconductor wafer in which a dopantevaporation preventive film is formed on one of main surfaces, whereinin that a film serving as the dopant evaporation preventive film isformed on the one of the main surfaces by a plasma CVD method, and theother main surface is then polished; and

4) a method of manufacturing a semiconductor wafer in which a dopantevaporation preventive film is formed on one of main surfaces and asemiconductor thin film is formed on the other main surface by epitaxialgrowth, wherein a film serving as the dopant evaporation preventive filmis formed on the one of the main surfaces by a plasma CVD method, thesemiconductor wafer is subject to heat treatment at a temperature lowerthan a temperature at which the expitaxial growth of the semiconductorthin film is carried out, and the other main surface is then polished.

Preferably, the dopant evaporation preventive film is selected from agroup consisting of silicon oxide film, silicon nitride film and siliconoxynitride film.

Preferably, the dopant evaporation preventive film is formed such that astress between the dopant evaporation preventive film and thesemiconductor wafer becomes equal to or less than 1×10⁷ dyne/cm².

According to the above-described aspect of the present invention, it ispossible to provide a semiconductor wafer having a dopant evaporationpreventive film on the back surface of the wafer, in which the stressacting to the wafer and resultant warpage of the wafer can be decreasedeven when the wafer has a large diameter, while maintaining a uniformthickness distribution, a uniform resistivity distribution and a narrowtransition width of an epitaxial layer grown on the semiconductor wafer,and in which the front surface of the semiconductor wafer can have anexcellent flatness without requiring an extra process.

Another aspect of the present invention, there are provided thefollowing methods of manufacturing a semiconductor wafer:

5) a method of manufacturing a semiconductor wafer having a plasma CVDfilm on one of main surfaces, wherein the plasma CVD film is formed onthe one of the main surfaces of the semiconductor wafer so that a stressbetween the plasma CVD film and the semiconductor wafer falls in a rangeof 1×10⁸ -1×10⁹ dyne/cm² ; and

6) a method of manufacturing a semiconductor wafer having a plasma CVDfilm on one of main surfaces, wherein the plasma CVD film is formed onthe one of the main surfaces of the semiconductor wafer, and thesemiconductor wafer is then subjected to heat treatment so that a stressbetween the plasma CVD film and the semiconductor wafer falls in a rangeof 1×10⁸ -1×10⁹ dyne/cm².

The other main surface of the semiconductor wafer on which the plasmaCVD film has not been formed is generally polished after the formationof the plasma CVD film or after the heat treatment of the semiconductorwafer. In the method of the present aspect, however, the plasma CVD filmmay be formed on the one of the main surfaces after the other mainsurface has been mirror-polished.

Preferably, the plasma CVD film is selected from a group consisting ofsilicon oxide film, silicon nitride film and silicon oxynitride film,because these films have excellent autodoping preventing effects, andtheir source gases are generally available.

According to the aspect of the present invention, it is possible toprovide a semiconductor wafer which has an excellently persistentgettering capability and an autodoping preventive capability and a smallstress acting thereon with a resultant small warpage thereof.

According to another aspect of the present invention, there are provideda semiconductor wafer manufactured by one of the above-described method,and a semiconductor epitaxial wafer manufactured by one of theabove-described method in which a semiconductor thin film is formed byepitaxial growth, on the other main surface of the semiconductor waferon which the plasma CVD film is not formed.

According to still another aspect of the present invention, there isprovided a method of manufacturing a semiconductor epitaxial wafer,wherein a plasma CVD film is formed on one of main surfaces of asemiconductor wafer, and a semiconductor thin film is formed byepitaxial growth on the other main surface on which the plasma CVD filmis not formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are schematic diagrams showing a method of manufacturing asemiconductor wafer according to the present invention;

FIG. 1D is a schematic diagram showing an epitaxial wafer manufacturedusing the semiconductor wafer shown in FIG. 1C;

FIGS. 2A-2D are schematic diagram showing another method ofmanufacturing a semiconductor wafer according to the present invention,wherein the portion above a broken line in FIG. 2D indicates a portionto be removed by mirror polishing; and

FIGS. 3A-3D are schematic diagram showing a method of manufacturing asilicon epitaxial wafer according to the present invention, wherein theportion above a broken line in FIG. 3C indicates a portion to be removedby mirror polishing.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the drawings.

First Embodiment

First, a semiconductor wafer 1 manufactured by a known method isprepared as shown in FIG. 1A. For this semiconductor wafer, achemically-etched wafer that has not yet been subjected tomirror-polishing is normally used, but a polished wafer having one orboth of the main surfaces thereof mirror polished might alternatively beused.

Subsequently, as shown in FIG. 1B, a plasma CVD film 2 is deposited onone of the main surfaces of the thus-prepared semiconductor wafer byusing a parallel-plate-type plasma CVD system. Although the kind ofplasma CVD film to be deposited on the wafer is not limited, siliconoxide film, silicon nitride film or silicon oxynitride film is suitablebecause these films can be formed by using gases of generally available.

The deposition conditions are controlled such that the depositiontemperature falls within the range of 300°-450° C., the depositionpressure falls within the range of 1-10 torr, and the deposition filmthickness falls within the range of 100-500 nm, and so that the stressof the plasma CVD film applied to the semiconductor wafer preferablybecomes equal to or less than 1×10⁷ dyne/cm². The magnitude of thestress can be measured in a non-destructive manner by use of acommercially available laser Raman spectrophotometer, which projects alaser beam onto the plasma CVD film.

After the deposition of the plasma CVD film, as shown in FIG. 1C, theother main surface opposite to the surface on which the plasma CVD hasbeen deposited is mirror-polished, whereby a desired semiconductor waferhaving an autodoping preventive film can be obtained. Since the plasmaCVD film deposited on the surface can be polished off at a much higherspeed as compared to the case where a thermal oxide film or anatmospheric pressure CVD oxide film is polished, the plasma CVD film canbe easily removed by mirror polishing. Consequently, the flatness of thesemiconductor wafer can be maintained.

In the case where the surface opposite to the surface on which a plasmaCVD film is to be deposited has been mirror-finished, a subsequentpolishing process can be omitted if the plasma CVD is prevented fromdepositing on the mirror-finished surface.

Moreover, as shown in FIG. 1D, an epitaxial layer 3 is grown on thesemiconductor wafer obtained through the above-described steps, at a lowtemperature equal to or less than 1000° C. and by use of a commerciallyavailable epitaxial reactor, so that a desired epitaxial wafer with aslight warpage can be obtained.

When the wafer on which the plasma CVD has been deposited is heattreated, before the mirror-polishing step, at a temperature lower thanthe temperature of the subsequently-performed epitaxial growth, theplasma CVD film is baked and hardened, so that a protective film havinga higher autodoping preventive capability can be obtained. The reasonwhy the heat treatment temperature is set to a temperature lower thanthe expitaxial growth temperature is to reduce the stress caused by thehardened plasma CVD film onto the semiconductor wafer.

EXAMPLE 1

Three kinds of silicon wafers were prepared from a silicon ingotmanufactured by the Czochralski method (each wafer had a diameter of 200mm, a {100} main surface, a thickness of 750 μm, a p-type conductivity,and a resistivity of 0.01 Ω.cm). Plasma CVD films (either silicon oxidefilm, silicon nitride film or silicon oxynitride film) were deposited oneach of the first main surface of the wafers by use of a plasma CVDreactor using radio-frequency of 13.56 MHz (Concept-One, product ofNovellus Systems Inc.).

When a silicon oxide film was formed as a plasma CVD film, monosilaneand nitrous oxide were supplied as source materials to a plasma reactionchamber while nitrogen was used as a carrier gas, and the silicon oxidefilm was deposited until its thickness reached 500 nm at a growthtemperature of 425° C. and a growth pressure of 3 torr. At this time, ahigh frequency power of 700 W was supplied to an upper plate locatedabove a wafer in the plasma reaction chamber, while a low frequencypower of 300 W was supplied to a lower plate located below the wafer, sothat the stress of the silicon oxide film applied to the wafer becameequal to or less than 1×10⁷ dyne/cm².

When a silicon nitride film was formed as a plasma CVD film, monosilaneand ammonia were used as source materials. The formation of the siliconnitride film was carried out under the same conditions as for thesilicon oxide film until the thickness reached 100 nm so that the stressof the silicon nitride film applied to the wafer became equal to or lessthan 1×10⁷ dyne/cm².

When a silicon oxynitride film was formed as a plasma CVD film,monosilane, nitrous oxide, and ammonia were used as source materials.The formation of the silicon oxynitride film was carried out under thesame conditions as for the silicon oxide film until the thicknessreached 300 nm so that the stress of the silicon oxynitride film appliedto the wafer became equal to or less than 1×10⁷ dyne/cm².

The thus-obtained wafers of the three kinds were observed to have littlewarpage when the stress acting thereon was equal to or less than 1×10⁷dyne/cm².

Subsequently, the second surface of each wafer opposite to the firstsurface on which the plasma CVD was deposited was polished, and anepitaxial film having a thickness of 4 μm was grown at low-temperatureof 800° C. In each of the cases where any kinds of the plasma CVD filmsabove-mentioned were formed, the resistivity distribution of the siliconepitaxial layer within the wafer surface was equal to or less than ±5%.The transition width of the silicon epitaxial layer became equal to orless than the half of that of an epitaxial layer deposited at 1100° C.This occurred because dopant in the silicon wafer was prevented fromevaporating at the back surface of the wafer not to cause autodoping,and the solid-phase diffusion of the dopant into the epitaxial layer wasdecreased. The amount of an increase in the warpage of the wafer afterthe formation of the epitaxial layer compared to the warpage before theformation of the epitaxial layer was as low as 5 μm or less.

The resistivity was measured at nine points within the wafer surface,and the resistivity distribution was calculated in accordance with thefollowing equation:

    Resistivity distribution (%)=±(M-m)/(M+m)

where M is the maximum value of the measured resistivity, and m is theminimum value of the measured resistivity.

Second Embodiment

First, a semiconductor wafer 4 manufactured by a known method isprepared as shown in FIG. 2A. For this semiconductor wafer, achemically-etched wafer that has not yet been subjected tomirror-polishing is generally used. However, a polished wafer having onemain surface or both main surfaces thereof mirror polished may be used.

Subsequently, as shown in FIG. 2B, a plasma CVD film 5 is deposited onone of main surfaces of the thus-prepared semiconductor wafer by use ofa parallel-plate-type plasma CVD reactor so that the stress of theplasma CVD film applied to the semiconductor wafer falls within a rangeof 1×10⁸ -1×10⁹ dyne/cm².

The reason why the plasma CVD film 5 is deposited so that the stressacting to the semiconductor wafer falls within the range of 1×10⁸ -1×10⁹dyne/cm² is that such stress creates strained layer which capturesimpurities such as metals, thereby serving as a gettering layer. Whenthe stress is less than 1×10⁸ dyne/cm², sufficient gettering capabilitycannot be obtained. When the stress is greater than 1×10⁹ dyne/cm², thewarpage of the wafer increases. The magnitude of the stress can bemeasured in a non-destructive manner by use of a commercially availablelaser Raman spectrophotometer, which projects a laser beam onto theplasma CVD film.

Although there is no limitation on the kind of plasma CVD film to bedeposited on the wafer, silicon oxide film, silicon nitride film orsilicon oxynitride film is suitable because these films have anautodoping preventive capability and can be formed by use of generallyavailable gasses.

The deposition of the plasma CVD film is usually performed such that thedeposition temperature falls within a range of 300°-450° C., thedeposition pressure falls within a range of 1-10 torr, and thedeposition film thickness falls within a range of 100-500 nm. Withinthese ranges, the deposition conditions are controlled so that thestress which the plasma CVD film applies to the semiconductor waferfalls within a range of 1×10⁸ -1×10⁹ dyne/cm².

Alternatively, after the deposition of the plasma CVD film 5, thesilicon wafer may be subjected to heat treatment so that the stressacting between the plasma CVD film and the semiconductor wafer fallswithin a range of 1×10⁸ -1×10⁹ dyne/cm², thereby forming a strainedlayer 6 as shown in FIG. 2C.

Even when the thus-formed plasma CVD film undergoes heat treatmentduring fabrication of semiconductor devices, the stress acting to thesemiconductor wafer does not decrease but rather increase slightly, sothat the gettering capability does not decrease.

After the deposition of the plasma CVD film or after heat treatment, theother main surface opposite to the main surface on which the plasma CVDhas been deposited is mirror-polished, whereby there can be obtained adesired semiconductor wafer which has an excellently persistentgettering capability, an autodoping preventive capability and smallstress acting to the wafer with a resultant small warpage thereof (seeFIG. 2D). Since the plasma CVD film deposited on the surface can bepolished off at much higher speed as compared to the case where athermal oxide film or an atmospheric pressure CVD oxide film ispolished, the plasma CVD film can be easily removed by mirror polishing.Consequently, the flatness of the semiconductor wafer can be maintained.

In the case where the surface opposite to the surface on which a plasmaCVD film is to be deposited has been mirror-finished, a subsequentpolishing process can be omitted if the plasma CVD is prevented fromdepositing on the mirror-finished surface.

Moreover, an epitaxial layer may be grown on the semiconductor waferobtained through the above-described steps by use of a commerciallyavailable epitaxial reactor, so that there can be obtained a desiredepitaxial wafer which has an excellently persistent getteringcapability, an autodoping preventive capability, and a small stressacting to the wafer with a resultant small warpage thereof.

The epitaxial growth process may be used as a replacement of heattreatment given to the semiconductor wafer on which the plasma CVD filmis deposited. That is, a semiconductor wafer 4 is prepared as shown inFIG. 3A, and a plasma CVD film 5 is deposited on the first main surfaceof the semiconductor wafer 4, as shown in FIG. 3B. Subsequently, thesecond main surface of the semiconductor wafer 4 opposite the first mainsurface on which the plasma CVD film 5 has been deposited is mirrorpolished, as shown in FIG. 3C. After that, an epitaxial layer 7 is grownon the mirror-polished second main surface. The epitaxial growth isconducted at a temperature in a range of 800°-1200°, whereby the stresswhich the plasma CVD film applies to the semiconductor wafer fallswithin a range of 1×10⁸ -1×10⁹ dyne/cm². As a result, the portions thatreceive the stress form a strained layer 6, as shown in FIG. 3D.

EXAMPLE 2

Four kinds of silicon wafers were prepared from a silicon ingotmanufactured by the Czochralski method (each wafer had a diameter of 150mm, a {100} main surface, a thickness of 630 μm, a p-type conductivity,and a resistivity of 0.01 Ω.cm). Silicon oxide film, silicon nitridefilm or silicon oxynitride film were respectively deposited, as a plasmaCVD film, on the first main surfaces of three kinds of wafers by use ofa plasma CVD reactor using radio-frequency of 13.56 MHz (Concept-one,product of Novellus Systems Inc.). The remaining one kind of wafer wasused as it was without forming the plasma CVD film.

When a silicon oxide film was formed as a plasma CVD film, monosilaneand nitrous oxide were supplied as source materials to a plasma reactionchamber while nitrogen was used as a carrier gas, and the silicon oxidefilm was deposited until its thickness reached 500 nm at a growthtemperature of 425° C. and a growth pressure of 3 torr. At this time, ahigh frequency power of 700 W was supplied to an upper plate locatedabove a wafer in the plasma reaction chamber, while a low frequencypower of 300 W was supplied to a lower plate located below the wafer, sothat the stress of the silicon oxide film applied to the wafer becameequal to 1×10⁸ dyne/cm².

When a silicon nitride film was formed as a plasma CVD film, monosilaneand ammonia were used as source materials. The formation of the siliconnitride film was carried out under the same conditions as for thesilicon oxide film until the thickness reached 100 nm so that the stressof the silicon nitride film applied to the wafer became equal to 1×10⁸dyne/cm².

When a silicon oxynitride film was formed as a plasma CVD film,monosilane, nitrous oxide and ammonia were used as source materials. Theformation of the silicon oxynitride film was carried out under the sameconditions as for the silicon oxide film until the thickness reached 300nm so that the stress of the silicon oxynitride film applied to thewafer became equal to 1×10⁸ dyne/cm².

The thus-obtained wafers of three kinds had warpages not greater than 3μm when the stress acting thereon was 1×10⁸ dyne/cm².

Subsequently, the second surface of each wafer opposite to the firstsurface on which the plasma CVD was deposited was polished, and anepitaxial film having a thickness of 5 μm was grown at 1100° C. In eachof the cases where any kind of the plasma CVD films above-mentioned wereformed, the resistivity distribution of the silicon epitaxial layerwithin the wafer surface was equal to or less than 15%. The transitionwidth (the width of a region which is located in the vicinity of theboundary between an epitaxial layer and a silicon wafer, each having adifferent dopant concentration, and in which a dopant concentrationtransits) of the silicon epitaxial layer became about half of that of anepitaxial layer deposited on a wafer having no plasma CVD film.

The resistivity was measured at nine points within the wafer surface,and the resistivity distribution was calculated in accordance with thefollowing equation:

    Resistivity distribution (%)=±(M-m)/(M+m)

where M is the maximum value of the measured resistivity, and m is theminimum value of the measured resistivity.

Measurement about the gettering capability was performed as follows. Aniron-containing solution was applied to the surface of each of fourkinds of wafers that were manufactured under the same conditions asabove-described, so that the thus-coated surface of each silicon waferwas intentionally contaminated. Thereafter, the silicon wafers weresubjected to heat treatment at a temperature of 1000° C. for one hour,so that iron was diffused into the silicon wafers. Subsequently, thesilicon wafers were further subjected to heat treatment at a temperatureof 650° C. for ten hours. A silicon wafer intentionally contaminatedwith iron is dissolved through etching, and the concentration of iron inthe solution is measured by chemical analysis. Then, the concentrationof iron in each silicon wafer with exclusion of the plasma CVD film wasmeasured.

By using the concentration of iron in the silicon wafer having no plasmaCVD film as a reference, a ratio of iron captured by the plasma CVD filmwas calculated from a measurement value of the iron concentration. Thethus-calculated ratio was used as a measure of gettering capability. Theresults revealed that the gettering capability of the semiconductorwafer on which a plasma CVD film was formed according to the presentinvention was 93-96%.

As is evident from the test result, the semiconductor wafer on which aplasma CVD film was formed according to the present invention had anexcellently persistent gettering capability and an autodoping preventivecapability.

Moreover, the amount of an increase in the warpage of the wafer afterthe formation of the epitaxial layer compared to the warpage before theformation of the epitaxial layer was as low as 5 μm or less. Thisdemonstrates that the semiconductor wafer on which a plasma CVD film wasformed according to the present invention had a reduced warpage ascompared to the warpage observed when more conventional autodoping filmsare used.

The present invention is not limited to the above-described embodiment.The above-described embodiment is a mere example, and those having thesubstantially same structure as that described in the appended claimsand providing the similar action and effects are included in the scopeof the present invention.

What is claimed is:
 1. A method of manufacturing a semiconductor waferwhich has a dopant evaporation preventive film formed on one of mainsurfaces thereof, said method comprising the step of:forming a plasmaCVD film that serves as the dopant evaporation preventive film on theone of the main surfaces by a plasma CVD method, said plasma CVD filmbeing formed from silicon oxide such that the stress between the plasmaCVD film and the semiconductor wafer becomes equal to or less than 1×10⁷dyne/cm².
 2. A method of manufacturing a semiconductor wafer in which adopant evaporation preventive film is formed on one of main surfaces anda semiconductor thin film is formed on the other main surface byepitaxial growth, said method comprising the steps of:forming a plasmaCVD film that serves as a dopant evaporation preventive film on the oneof the main surfaces by a plasma CVD method, said plasma CVD film beingformed from silicon oxide such that the stress between the plasma CVDfilm and the semiconductor wafer becomes equal to or less than 1×10⁷dyne/cm² ; and heat-treating the semiconductor wafer at a temperaturelower than a temperature at which the epitaxial growth of thesemiconductor thin film is carried out.
 3. A method of manufacturing asemiconductor wafer in which a dopant evaporation preventive film isformed on one of main surfaces, said method comprising the stepsof:forming a plasma CVD film that serves as the dopant evaporationpreventive film on the one of the main surfaces by a plasma CVD method,said plasma CVD film being formed from silicon oxide such that thestress between the plasma CVD film and the semiconductor wafer becomesequal to or less than 1×10⁷ dyne/cm² ; and polishing the other mainsurface.
 4. A method of manufacturing a semiconductor wafer in which adopant evaporation preventive film is formed on one of main surfaces anda semiconductor thin film is formed on the other main surface byepitaxial growth, said method comprising the steps of:forming a plasmaCVD film that serves as the dopant evaporation preventive film on theone of the main surfaces by a plasma CVD method, said plasma CVD filmbeing formed from silicon oxide such that the stress between the plasmaCVD film and the semiconductor wafer becomes equal to or less than 1×10⁷dyne/cm² ; heat-treating the semiconductor wafer at a temperature lowerthan a temperature at which the epitaxial growth of the semiconductorthin film is carried out; and polishing the other main surface.
 5. Amethod of manufacturing a semiconductor wafer having a plasma CVD filmon one of main surfaces, wherein the plasma CVD film is formed fromsilicon nitride on one of the main surfaces of the semiconductor waferso that a stress between the plasma CVD film and the semiconductor waferfalls in a range of 1×10⁸ -1×10⁹ dyne/cm².
 6. A method of manufacturinga semiconductor wafer according to claim 5, wherein the other mainsurface of the semiconductor wafer on which the plasma CVD film has notbeen formed is polished after the formation of the plasma CVD film.
 7. Amethod of manufacturing a semiconductor wafer according to claim 5,wherein the plasma CVD film is formed on one of main surfaces of thewafer after the other main surface has been mirror-polished.
 8. A methodof manufacturing a semiconductor wafer having a plasma CVD film on oneof main surfaces, said method comprising the steps of:forming a plasmaCVD film from silicon nitride on the one of the main surfaces of thesemiconductor wafer; and heat-treating the semiconductor wafer so that astress between the plasma CVD film and the semiconductor wafer falls ina range of 1×10⁸ -1×10⁹ dyne/cm².
 9. A method of manufacturing asemiconductor wafer according to claim 8, wherein the other main surfaceof the semiconductor wafer on which the plasma CVD film has not beenformed is polished after the semiconductor wafer is subjected to heattreatment.
 10. A method of manufacturing a semiconductor wafer accordingto claim 8, wherein the plasma CVD film is formed on one of the mainsurfaces of the wafer after at least the other main surface has beenmirror-polished.
 11. A semiconductor wafer manufactured by the methoddescribed in claim
 1. 12. A semiconductor epitaxial wafer in which asemiconductor thin film is formed by epitaxial growth, on one of mainsurfaces of the semiconductor wafer manufactured by the method describedin claim 1, wherein the plasma CVD film is not formed on the one of themain surfaces.
 13. A method of manufacturing a semiconductor epitaxialwafer, said method comprising the steps of:forming a plasma CVD filmfrom silicon oxide on one of main surfaces of a semiconductor wafer suchthat the stress between the plasma CVD film and the semiconductor waferbecomes equal to or less than 1×10⁷ dyne/cm² ; heat-treating thesemiconductor wafer at a predetermined temperature; polishing the othermain surface of the semiconductor wafer; and forming a semiconductorthin film by epitaxial growth on the other main surface at a temperatureequal to or less than 1000° C., wherein the predetermined temperaturefor the heat treatment is lower than the temperature for epitaxialgrowth of the semiconductor thin film, and wherein the above-describedsteps are performed in this sequence.
 14. A method of manufacturing asemiconductor epitaxial wafer comprising the step of:growing, throughepitaxial growth, a semiconductor thin film on the one of the mainsurfaces, on which the plasma CVD film is not formed, of a semiconductorwafer manufactured in accordance with the method according to claim 5.15. A method of manufacturing a semiconductor epitaxial wafer comprisingthe step of:growing, through epitaxial growth, a semiconductor thin filmon the one of the main surfaces, on which the plasma CVD film is notformed, of a semiconductor wafer manufactured in accordance with themethod according to claim 8.